Author: Alan Ding <alanding@google.com>
Date:   Tue May 18 15:21:14 2021 -0700

    ureadahead: Add --force-ssd-mode option for vms
    
    Adds command line option: --force-ssd-mode (off by default).
    Querying sysfs to detect whether disk is rotational does not work for
    virtual devices in vm, and if set will write pack header with rotational
    field set to 0. This option will remove running unnecessary code
    intended for hdd; any attempts to set highest priority (IOPRIO_CLASS_RT)
    requiring CAP_SYS_ADMIN capability which ARCVM SELinux will deny.
    
    There is no functional effect if option is not used.

diff --git a/src/trace.c b/src/trace.c
index 854a570..f337f0a 100644
--- a/src/trace.c
+++ b/src/trace.c
@@ -92,13 +92,13 @@ static int       read_trace        (const void *parent,
 				    int dfd, const char *path,
 				    const char *path_prefix_filter,
 				    const PathPrefixOption *path_prefix,
-				    PackFile **files, size_t *num_files);
+				    PackFile **files, size_t *num_files, int force_ssd_mode);
 static void      fix_path          (char *pathname);
 static int       trace_add_path    (const void *parent, const char *pathname,
-				    PackFile **files, size_t *num_files);
+				    PackFile **files, size_t *num_files, int force_ssd_mode);
 static int       ignore_path       (const char *pathname);
 static PackFile *trace_file        (const void *parent, dev_t dev,
-				    PackFile **files, size_t *num_files);
+				    PackFile **files, size_t *num_files, int force_ssd_mode);
 static int       trace_add_chunks  (const void *parent,
 				    PackFile *file, PackPath *path,
 				    int fd, off_t size);
@@ -123,7 +123,8 @@ trace (int daemonise,
        const char *pack_file,
        const char *path_prefix_filter,
        const PathPrefixOption *path_prefix,
-       int debug_tracing)
+       int debug_tracing,
+	   int force_ssd_mode)
 {
 	int                 dfd;
 	FILE                *fp;
@@ -262,7 +263,7 @@ trace (int daemonise,
 
 	/* Read trace log */
 	if (read_trace (NULL, dfd, "trace", path_prefix_filter, path_prefix,
-			&files, &num_files) < 0)
+			&files, &num_files, force_ssd_mode) < 0)
 		goto error;
 
 	/*
@@ -349,7 +350,8 @@ read_trace (const void *parent,
 	    const char *path_prefix_filter,  /* May be null */
 	    const PathPrefixOption *path_prefix,
 	    PackFile ** files,
-	    size_t *    num_files)
+	    size_t *    num_files,
+		int         force_ssd_mode)
 {
 	int   fd;
 	FILE *fp;
@@ -423,7 +425,7 @@ read_trace (const void *parent,
 				ptr = rewritten;
 			}
 		}
-		trace_add_path (parent, ptr, files, num_files);
+		trace_add_path (parent, ptr, files, num_files, force_ssd_mode);
 
 		nih_free (line);  /* also frees |rewritten| */
 	}
@@ -486,7 +488,8 @@ static int
 trace_add_path (const void *parent,
 		const char *pathname,
 		PackFile ** files,
-		size_t *    num_files)
+		size_t *    num_files,
+		int         force_ssd_mode)
 {
 	static NihHash *path_hash = NULL;
 	struct stat     statbuf;
@@ -580,7 +583,7 @@ trace_add_path (const void *parent,
 	 * Lookup file based on the dev_t, potentially creating a new
 	 * pack file in the array.
 	 */
-	file = trace_file (parent, statbuf.st_dev, files, num_files);
+	file = trace_file (parent, statbuf.st_dev, files, num_files, force_ssd_mode);
 
 	/* Grow the PackPath array and fill in the details for the new
 	 * path.
@@ -670,7 +673,8 @@ static PackFile *
 trace_file (const void *parent,
 	    dev_t       dev,
 	    PackFile ** files,
-	    size_t *    num_files)
+	    size_t *    num_files,
+		int         force_ssd_mode)
 {
 	nih_local char *filename = NULL;
 	int             rotational;
@@ -684,30 +688,34 @@ trace_file (const void *parent,
 		if ((*files)[i].dev == dev)
 			return &(*files)[i];
 
-	/* Query sysfs to see whether this disk is rotational; this
-	 * obviously won't work for virtual devices and the like, so
-	 * default to TRUE for now.
-	 */
-	filename = NIH_MUST (nih_sprintf (NULL, "/sys/dev/block/%d:%d/queue/rotational",
-					  major (dev), minor (dev)));
-	if (access (filename, R_OK) < 0) {
-		/* For devices managed by the scsi stack, the minor device number has to be
-		 * masked to find the queue/rotational file.
+	if (force_ssd_mode) {
+		rotational = FALSE;
+	} else {
+		/* Query sysfs to see whether this disk is rotational; this
+		 * obviously won't work for virtual devices and the like, so
+		 * default to TRUE for now.
 		 */
-		nih_free (filename);
 		filename = NIH_MUST (nih_sprintf (NULL, "/sys/dev/block/%d:%d/queue/rotational",
-						  major (dev), minor (dev) & 0xffff0));
-	}
+						major (dev), minor (dev)));
+		if (access (filename, R_OK) < 0) {
+			/* For devices managed by the scsi stack, the minor device number has to be
+			 * masked to find the queue/rotational file.
+			 */
+			nih_free (filename);
+			filename = NIH_MUST (nih_sprintf (NULL, "/sys/dev/block/%d:%d/queue/rotational",
+							major (dev), minor (dev) & 0xffff0));
+		}
 
-	if (get_value (AT_FDCWD, filename, &rotational) < 0) {
-		NihError *err;
+		if (get_value (AT_FDCWD, filename, &rotational) < 0) {
+			NihError *err;
 
-		err = nih_error_get ();
-		nih_warn (_("Unable to obtain rotationalness for device %u:%u: %s"),
-			  major (dev), minor (dev), err->message);
-		nih_free (err);
+			err = nih_error_get ();
+			nih_warn (_("Unable to obtain rotationalness for device %u:%u: %s"),
+				major (dev), minor (dev), err->message);
+			nih_free (err);
 
-		rotational = TRUE;
+			rotational = TRUE;
+		}
 	}
 
 	/* Grow the PackFile array and fill in the details for the new
diff --git a/src/trace.h b/src/trace.h
index f809cc6..8d60b0a 100644
--- a/src/trace.h
+++ b/src/trace.h
@@ -38,7 +38,8 @@ int trace (int daemonise, int timeout,
            const char *pack_file,  /* May be null */
            const char *path_prefix_filter,  /* May be null */
            const PathPrefixOption *path_prefix,
-           int debug_tracing);
+           int debug_tracing,
+           int force_ssd_mode);
 
 NIH_END_EXTERN
 
diff --git a/src/ureadahead.c b/src/ureadahead.c
index d1bf5a1..61130d4 100644
--- a/src/ureadahead.c
+++ b/src/ureadahead.c
@@ -118,6 +118,14 @@ static char *path_prefix_filter = NULL;
  */
 static int no_debug_tracing = FALSE;
 
+/**
+ * force_ssd_mode:
+ *
+ * Querying sysfs to detect whether disk is rotational does not work for virtual
+ * devices in vm, this will write pack header with rotational field set to 0.
+ */
+static int force_ssd_mode = FALSE;
+
 static int
 path_prefix_option (NihOption  *option,
                     const char *arg)
@@ -221,6 +229,8 @@ static NihOption options[] = {
 	  NULL, "PACK_FILE", &pack_file, dup_string_handler },
 	{ 0, "no-debug-tracing", N_("do not enable debug tracing events"),
 	  NULL, NULL, &no_debug_tracing, NULL },
+	{ 0, "force-ssd-mode", N_("force ssd setting in pack file during tracing"),
+	  NULL, NULL, &force_ssd_mode, NULL },
 
 	NIH_OPTION_LAST
 };
@@ -311,7 +321,8 @@ main (int   argc,
 
 	/* Trace to generate new pack files */
 	if (trace (daemonise, timeout, filename, pack_file,
-		   path_prefix_filter, &path_prefix, (no_debug_tracing == FALSE)) < 0) {
+		   path_prefix_filter, &path_prefix, (no_debug_tracing == FALSE),
+		   force_ssd_mode) < 0) {
 		NihError *err;
 
 		err = nih_error_get ();